Calendars can be synced (and un-synced) on a project-level. Removing the calendar sync feature from your project dashboard will remove all sessions from your personal calendar.
Here's how to deactivate this functionality:
- Log into your account.
- Visit your project dashboard.
- In the left hand menu find the Schedule section.
- Click "Manage availability".
- Click the "Disconnect" link to remove the calendar sync located in the text (see image below).
- Be sure to save your changes, if prompted.